1. Field of the Invention
The present invention relates to a washing machine, and more particularly, to washing machine having an apparatus for controlling a dewatering step, in which a vibration detector is utilized to avoid a re-initialization of a dewatering step due to a resonance vibration.
2. Discussion of the Related Art
In the dewatering step of a washing machine, which typically requires high-rate rotation (spinning) of a drum, eccentricity is an important issue. Eccentricity is usually caused by an asymmetrical distribution of laundry within the drum, which is being rotated by a motor, and excessive eccentricity will generate undue levels of vibration and noise. Therefore, eccentricity must be carefully monitored so the motor speed, typically measured in revolutions per minute (rpm), may be regulated to control the rotational speed of the dewatering step. For excessive amounts of eccentricity, the motor is stopped.
An apparatus for controlling a dewatering step in a washing machine according to a related art, as shown in FIG. 1, includes a motor 1, an eccentricity detector 2 for detecting an amount of eccentricity present during the execution of a dewatering step, and a microcomputer 3 for controlling the motor 1 and specifically for stopping the motor if the detected amount of eccentricity exceeds a predetermined level. The microcomputer 3 is provided with an internal memory (not shown), in which a lookup table is stored.
In the operation of the above apparatus, upon executing a dewatering step in the washing machine according to the related art, the microcomputer 3 controls the motor 1 to be accelerated to a predetermined rate or rpm, which is gradually increased until reaching the desired dewatering speed. When the motor 1 reaches the predetermined rate, an amount of eccentricity is detected by the eccentricity detector 2, which takes the measure of the motor's rpm at intervals according to a detection control signal of the microcomputer 3, to thereby detect rpm variations. The periodically detected results are fed to the microcomputer 3 as an arbitrary number representing eccentricity for comparison with the data of the lookup table. The microcomputer 3 thus determines whether rpm variation is within a predetermined allowable range of eccentricity and outputs a motor control signal to the motor 1 based on the determination, thereby stopping the motor if the amount of eccentricity exceeds the predetermined allowable range or otherwise further accelerating the motor. Assuming that amount of eccentricity continues to fall within the predetermined range as the eccentricity detection is repeated periodically according to a predetermined cycle, further accelerations will cause the motor 1 to reach a desired dewatering speed as determined by user operation.
The lookup table of the microcomputer 3 includes data for an allowable range of eccentricity (reference eccentricity), desired dewatering speed, and a number n of periodic eccentricity detections. Importantly, the allowable range of eccentricity and the dewatering speed both vary in steps as the periodic eccentricity detection number progresses, with the reference eccentricity allowing for greater amounts of eccentricity for slower dewatering speeds. An example of such a lookup table is shown in Table 1 below.
TABLE 1eccentricity detection number (n)1~56~1010~1516~20reference eccentricity20253035desired dewatering speed (rpm)120011001000800
Referring to FIG. 2, illustrating a washing machine control method according to a related art, the microcomputer 3 accelerates the motor 1 to a predetermined dewatering speed (rpm) in a step S1, and according to the microcomputer's detection control signal, the eccentricity detector 2 periodically detects in a step S2 the dewatering speed as the motor is accelerated. The predetermined rate of the motor 1 for the initial detection of eccentricity is, for example, 100 rpm, which is the n=1 condition. The eccentricity detection number n is incremented in a step S3 and continues to be incremented until the desired dewatering speed is reached.
In a step S4, it is determined whether the detected eccentricity at the accelerated motor speed corresponding to eccentricity detection n is acceptable with respect to the reference eccentricity of Table 1. If so, the acceleration rate of the motor 1 is controlled in a step S5, gradually increasing to the desired dewatering speed while incrementing the eccentricity detection number. Initially, the eccentricity detection number is “1” so that the reference eccentricity is “20” and the desired dewatering speed is 1200 rpm.
On the other hand, if it is determined that the detected eccentricity exceeds the reference eccentricity, the motor 1 is stopped in a step S6 and the dewatering step is reinitialized. In doing so, the rotational rate of the motor 1 decelerates as necessary and the eccentricity number is reset to “1.”
The above washing machine according to the related art, however, has a significant problem with resonance vibration, which is an inherent problem in dewatering washing machines. As the dewatering step progresses, a resonance vibration occurring at motor rates of about 150˜300 rpm naturally interferes with the rate of eccentricity detection, regardless of dewatering speed control. In addition to undesired levels of noise, the resonance vibration produces eccentricity, such that the reference eccentricity values of the lookup table must be set low, which repeatedly interrupts the acceleration of the motor and thus impedes dewatering and increases washing time accordingly.